Browsing by Author "Sonti, Ramesh V."

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Co-overexpression of SWEET sucrose transporters modulates sucrose synthesis and defence responses to enhance immunity against bacterial blight in rice
(John Wiley & Sons, 2024) Singh, Jitender; James, Donald; Das, Shubhashis; Patel, Manish Kumar; Sutar, Rashmi Ranjan; Achary, V. Mohan Murali; Goel, Naveen; Gupta, Kapuganti Jagadis; Reddy, Malireddy K.; Jha, Gopaljee; Sonti, Ramesh V.; Foyer, Christine H.; Thakur, Jitendra K.; Tripathy, Baishnab C.
Enhancing carbohydrate export from source to sink tissues is considered to be a realistic approach for improving photosynthetic efficiency and crop yield. The rice sucrose transporters OsSUT1, OsSWEET11a and OsSWEET14 contribute to sucrose phloem loading and seed filling. Crucially, Xanthomonas oryzae pv. oryzae (Xoo) infection in rice enhances the expression of OsSWEET11a and OsSWEET14 genes, and causes leaf blight. Here we show that co‐overexpression of OsSUT1, OsSWEET11a and OsSWEET14 in rice reduced sucrose synthesis and transport leading to lower growth and yield but reduced susceptibility to Xoo relative to controls. The immunity‐related hypersensitive response (HR) was enhanced in the transformed lines as indicated by the increased expression of defence genes, higher salicylic acid content and presence of HR lesions on the leaves. The results suggest that the increased expression of OsSWEET11a and OsSWEET14 in rice is perceived as a pathogen (Xoo) attack that triggers HR and results in constitutive activation of plant defences that are related to the signalling pathways of pathogen starvation. These findings provide a mechanistic basis for the trade‐off between plant growth and immunity because decreased susceptibility against Xoo compromised plant growth and yield.
Complete genome dynamics of a dominant-lineage strain of Xanthomonas oryzae pv. oryzae harbouring a novel plasmid encoding a type IV secretion system
(Microbiology Society, 2019) Kaur, Amandeep; Bansal, Kanika; Kumar, Sanjeet; Sonti, Ramesh V.; Patil, Prabhu B.
Xanthomonas oryzae pv. oryzae (Xoo) is a serious pathogen causing bacterial blight disease in rice. Population genomic studies have revealed that rampant inter-strain rather than inter-lineage differences are contributing to the evolutionary success of this pathogen. Here, we report the complete genome sequence of BXO1, a strain of Xoo belonging to a dominant lineage from India. A complete genome-based investigation revealed the presence of two plasmids, pBXO1-1 (66.7kb) and pBXO1-2 (25.6kb). The pBXO1-1 plasmid encodes 71 genes, 38 of which encode hypothetical proteins of unknown function. However, these hypothetical genes possess atypical GC content, pointing towards their acquisition and movement through horizontal gene transfer. Interestingly, pBXO1-2 encodes a type IV secretion system (T4SS), which is known to play an important role in the conjugative transfer of genetic material, and also provides fitness to pathogenic bacteria for their enhanced survival. Neither plasmid has been reported previously in any other complete Xoo genome published to date. Our analysis also revealed that the pBXO1-2 plasmid is present in Xanthomonas albilineans str. GPE PC73, which is known to cause leaf scald, a lethal disease in sugarcane. Our complete genome sequence analysis of BXO1 has provided us with detailed insights into the two novel strain-specific plasmids, in addition to decoding their functional capabilities, which were not assessable when using the draft genome sequence of the strain. Overall, our study has revealed the mobility of a novel T4SS in two pathogenic species of Xanthomonas that infect the vascular tissues of two economically important monocot plants, i.e. rice and sugarcane.
Dual activities of receptor-like kinase OsWAKL21.2 induce immune responses
(American Society of Plant Biologists, 2020) Malukani, Kamal Kumar; Ranjan, Ashish; Hota, Shiva Jyothi; Patel, Hitendra Kumar; Sonti, Ramesh V.
Plant pathogens secrete cell wall-degrading enzymes that degrade various components of the plant cell wall. Plants sense this cell wall damage as a mark of infection and induce immune responses. However, the plant functions that are involved in the elaboration of cell wall damage-induced immune responses remain poorly understood. Transcriptome analysis revealed that a rice (Oryza sativa) receptor-like kinase, WALL-ASSOCIATED KINASE-LIKE21 (OsWAKL21.2), is up-regulated following treatment with either Xanthomonas oryzae pv oryzae (a bacterial pathogen) or lipaseA/esterase (LipA; a cell wall-degrading enzyme of X. oryzae pv oryzae). Overexpression of OsWAKL21.2 in rice induces immune responses similar to those activated by LipA treatment. Down-regulation of OsWAKL21.2 attenuates LipA-mediated immune responses. Heterologous expression of OsWAKL21.2 in Arabidopsis (Arabidopsis thaliana) also activates plant immune responses. OsWAKL21.2 is a dual-activity kinase that has in vitro kinase and guanylate cyclase activities. Interestingly, kinase activity of OsWAKL21.2 is necessary to activate rice immune responses, whereas in Arabidopsis, OsWAKL21.2 guanylate cyclase activity activates these responses. Our study reveals a rice receptor kinase that activates immune responses in two different species via two different mechanisms.
Ectopic expression of a cell-wall-degrading enzyme-induced OsAP2/ERF152 leads to resistance against bacterial and fungal infection in Arabidopsis
(The American Phytopathological Society, 2020) Pillai, Shakuntala E.; Kumar, Chandan; Dasgupta, Madhumita; Kumar, Bipin K.; Vungarala, Sridivya; Patel, Hitendra K.; Sonti, Ramesh V.
Pathogen secreted cell-wall-degrading enzymes (CWDEs) induce plant innate immune responses. The expression of rice transcription factor APETALA2/ethylene response factor-152 (OsAP2/ERF152) is enhanced in leaves upon treatment with different CWDEs and upon wounding. Ectopic expression of OsAP2/ERF152 in Arabidopsis leads to induction of immune responses such as callose deposition and upregulation of both salicylic acid- and jasmonic acid/ethylene-responsive defense genes. Arabidopsis transgenics expressing OsAP2/ERF152 exhibited resistance to infections caused by both bacterial and fungal pathogens (Pseudomonas syringae pv. tomato DC3000 and Rhizoctonia solani AG1-IA, respectively). Ectopic expression of OsAP2/ERF152 results in transient activation of mitogen-activated protein kinases 3/6 (MPK3/6), which could be leading to the induction of a broad range immunity in Arabidopsis.
Immune response induction in rice due to co-expression of XopQ and XopX
(American Phytopathological Society, 2019) Deb, S.; Patel, H. K.; Sonti, Ramesh V.
Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight, a serious disease of rice. Xoo uses the type III secretion system (T3SS) to suppress rice immune responses. The T3SS secreted effectors XopQ and XopX suppress rice immune responses by interaction with different rice 14-3-3 proteins. Sub-cellular localisation of XopQ and XopX mutants that are defective in 14-3-3 binding and suppression of immune responses indicates that, for suppression, XopQ requires a cytoplasmic localisation whereas XopX requires nuclear localisation. Hence, both XopQ as well as XopX individually act as suppressors of rice immune responses, probably by targeting unique pathways in different subcellular compartments. However, we find that when XopQ is delivered through Agrobacterium along with XopX, it becomes an inducer of immune responses and that it now localizes in the nucleus. We also find that XopQ and XopX can interact with each other. This raises the possibility that besides being a suppressor of immune responses, XopQ can under certain circumstances also function as an inducer of immune responses.
India needs genetic modification technology in agriculture
(Indian Academy of Sciences, 2019) Datta, S.; Dhillon, B. S.; Gautam, P. L.; Karihaloo, J. L.; Mahadevappa, M.; Mayee, C. D.; Padmanaban, G.; Parida, A.; Paroda, R. S.; Sharma, M.; Sharma, T. R.; Singh, N. K.; Singh, R. B.; Sonti, Ramesh V.; Tyagi, Akhilesh K.; Varma, A.; Veluthambi, K.
India does not have a clear stand on the release and consumption of genetically modified crops (food). The only approved crop is Bt-cotton, which has put India on the global map as a cotton exporting country. Even so, Bt-brinjal is under moratorium and GM mustard is prevented from undergoing commercial trial. All these decisions are not based on sound scientific principles. Activism against has successfully prevented exploitation of a powerful technology that can contribute to India’s food and nutrition security. This article attempts to give a balanced perspective of genetic modification technology as one of the serious options to be considered on case to case basis. Ambivalence will seriously affect India’s food security in the future.
An innovative root inoculation method to study Ralstonia solanacearum pathogenicity in tomato seedlings
(American Phytopathological Society, 2018) Singh, N.; Phukan, T.; Sharma, P.L.; Kabyashree, K.; Barman, A.; Kumar, R.; Sonti, Ramesh V.; Genin, S.; Ray, S.K.
In this study, we report Ralstonia solanacearum pathogenicity in the early stages of tomato seedlings by an innovative root inoculation method. Pathogenicity assays were performed under gnotobiotic conditions in microfuge tubes by employing only 6- to 7-day-old tomato seedlings for root inoculation. Tomato seedlings inoculated by this method exhibited the wilted symptom within 48 h and the virulence assay can be completed in 2 weeks. Colonization of the wilted seedlings by R. solanacearum was confirmed by using gus staining as well as fluorescence microscopy. Using this method, mutants in different virulence genes such as hrpB, phcA, and pilT could be clearly distinguished from wild-type R. solanacearum. The method described here is economic in terms of space, labor, and cost as well as the required quantity of bacterial inoculum. Thus, the newly developed assay is an easy and useful approach for investigating virulence functions of the pathogen at the seedling stage of hosts, and infection under these conditions appears to require pathogenicity mechanisms used by the pathogen for infection of adult plants.
Interaction of the Xanthomonas effectors XopQ and XopX results in induction of rice immune responses
(John Wiley & Sons, 2020) Deb, Sohini; Ghosh, Palash; Patel, Hitendra K.; Sonti, Ramesh V.
Xanthomonas oryzae pv. oryzae uses several type III secretion system (T3SS) secreted effectors, namely XopN, XopQ, XopX, and XopZ, to suppress rice immune responses that are induced following treatment with cell wall degrading enzymes. Here we show that a T3SS secreted effector XopX interacts with two of the eight rice 14‐3‐3 proteins. Mutants of XopX that are defective in 14‐3‐3 binding are also defective in suppression of immune responses, suggesting that interaction with 14‐3‐3 proteins is required for suppression of host innate immunity. However, Agrobacterium mediated delivery of both XopQ and XopX into rice cells results in induction of rice immune responses. These immune responses are not observed when either protein is individually delivered into rice cells. XopQ‐ XopX induced rice immune responses are not observed with a XopX mutant that is defective in 14‐3‐3 binding. Yeast two‐ hybrid, BiFC and co‐ IP assays indicate that XopQ and XopX interact with each other. A screen for Xanthomonas effectors which can suppress XopQ‐ XopX induced rice immune responses, led to the identification of five effectors, namely XopU, XopV, XopP, XopG and AvrBs2, that could individually suppress these immune responses. These results suggest a complex interplay of Xanthomonas T3SS effectors in suppression of both pathogen triggered immunity and effector triggered immunity to promote virulence on rice.
OsWAKL21, a putative receptor of rice cell wall damage activates alternate signaling in rice and Arabidopsis to induce immunity
(American Phytopathological Society, 2019) Malukani, K. K.; Ranjan, A.; Hota, S. J.; Patel, H. K.; Sonti, Ramesh V.
Xanthomonas oryzae pv. oryzae (Xoo) causes the serious bacterial blight disease of rice. As part of its virulence repertoire, Xoo secretes various cell wall degrading enzymes (CWDEs) such as cellulases, xylanases and a Lipase/esterase (LipA). Conversely, treatment of rice tissues with any of these purified enzymes activates immune responses. Plants sense this cell wall damage as a mark of infection and induce immune responses. Very little information is available about the plant functions that are involved in the elaboration of cell wall damage induced immune responses. Transcriptome analyses revealed a rice cell wall-associated receptor kinase, OsWAKL21 that is upregulated following treatment with either LipA or Xoo. VIGS mediated downregulation of OsWAKL21 attenuates LipA induced immune responses. Overexpression of OsWAKL21 in rice mimics LipA treatment in induction of immune responses, activation of JA pathway and enhanced expression of defence related genes, indicating that it plays an important role in elaboration of LipA induced immune responses. Ectopic expression of OsWAKL21 in Arabidopsis also activates plant immune responses. OsWAKL21 is a moonlighting kinase having in vitro kinase and guanylate cyclase activities. Interestingly, OsWAKL21 needs kinase activity to activate immune responses in rice while in Arabidopsis it needs the guanylate cyclase activity. Thus OsWAKL21 is activating similar immune responses in two different species but via different mechanisms.
Overexpression of a cell wall damage induced transcription factor, OsWRKY42, leads to enhanced callose deposition and tolerance to salt stress but does not enhance tolerance to bacterial infection
(BioMed Central Ltd, 2018) Pillai, Shakuntala E.; Kumar, Chandan; Patel, Hitendra K.; Sonti, Ramesh V.
Background: Members of the WRKY gene family play important roles in regulating plant responses to abiotic and biotic stresses. Treatment with either one of the two different cell wall degrading enzymes (CWDEs), LipaseA and CellulaseA, induces immune responses and enhances the expression of OsWRKY42 in rice. However, the role of OsWRKY42 in CWDE induced immune responses is not known. Results: Expression of the rice transcription factor OsWRKY42 is induced upon treatment of rice leaves with CWDEs, wounding and salt. Overexpression of OsWRKY42 leads to enhanced callose deposition in rice and Arabidopsis but this does not enhance tolerance to bacterial infection. Upon treatment with NaCl, Arabidopsis transgenic plants expressing OsWRKY42 exhibited high levels of anthocyanin and displayed enhanced tolerance to salt stress. Treatment with either cellulase or salt induced the expression of several genes involved in JA biosynthesis and response in Arabidopsis. Ectopic expression of OsWRKY42 results in reduced expression of cell wall damage and salt stress induced jasmonic acid biosynthesis and response genes. OsWRKY42 expressing Arabidopsis lines exhibited enhanced tolerance to methyl jasmonate mediated growth inhibition. Conclusion: The results presented here suggest that OsWRKY42 regulates plant responses to either cell wall damage or salinity stress by acting as a negative regulator of jasmonic acid mediated responses.
Overexpression of OsPUB41, a rice E3 ubiquitin ligase induced by cell wall degrading enzymes, enhances immune responses in rice and Arabidopsis
(BioMed Central Ltd, 2019) Kachewar, Neha Rajendra; Gupta, Vishal; Ranjan, Ashish; Patel, Hitendra Kumar; Sonti, Ramesh V.
Background: Cell wall degrading enzymes (CWDEs) induce plant immune responses and E3 ubiquitin ligases are known to play important roles in regulating plant defenses. Expression of the rice E3 ubiquitin ligase, OsPUB41, is enhanced upon treatment of leaves with Xanthomonas oryzae pv. oryzae (Xoo) secreted CWDEs such as Cellulase and Lipase/Esterase. However, it is not reported to have a role in elicitation of immune responses. Results: Expression of the rice E3 ubiquitin ligase, OsPUB41, is induced when rice leaves are treated with either CWDEs, pathogen associated molecular patterns (PAMPs), damage associated molecular patterns (DAMPs) or pathogens. Overexpression of OsPUB41 leads to induction of callose deposition, enhanced tolerance to Xoo and Rhizoctonia solani infection in rice and Arabidopsis respectively. In rice, transient overexpression of OsPUB41 leads to enhanced expression of PR genes and SA as well as JA biosynthetic and response genes. However, in Arabidopsis, ectopic expression of OsPUB41 results in upregulation of only JA biosynthetic and response genes. Transient overexpression of either of the two biochemically inactive mutants (OsPUB41C40A and OsPUB41V51R) of OsPUB41 in rice and stable transgenics in Arabidopsis ectopically expressing OsPUB41C40A failed to elicit immune responses. This indicates that the E3 ligase activity of OsPUB41 protein is essential for induction of plant defense responses. Conclusion: The results presented here suggest that OsPUB41 is possibly involved in elicitation of CWDE triggered immune responses in rice.
Phase variation in rice pathogen Xanthomonas oryzae pv. oryzae
(American Phytopathological Society, 2019) Madhavan, V. N.; Patel, H. K.; Patil, P. B.; Sonti, Ramesh V.
Xanthomonas oryzae pv. oryzae (Xoo) is the causal pathogen of bacterial blight of rice. Diverse factors contribute to its virulence, e.g., secreted enzymes, protein involved in adhesion, gene regulation. Two such studied virulence factors are Exopolysaccharide (EPS) and Lipopolysaccharide (LPS). LPS is a structural component of the outer membrane of all gram-negative bacteria. LPS is necessary for the function of many outer membrane proteins and protect the bacteria from antimicrobial plant products. EPS is a complex polymer secreted by Xanthomonas genus and the known functions of EPS include biofilm formation, and suppression of the plant immune responses. In this study, we isolated non-mucoid and virulence compromised Xoo colonies from stationary phase cultures. These spontaneous mutants are called as stationary phase variants (SPV). Our data show that, SPVs arises due to insertion of endogenous Insertion Sequence (IS) elements in EPS or LPS O-antigen biosynthetic clusters or by slipped-strand mispairing (SSM) in wxoA gene of LPS O-antigen biosynthetic cluster. The SPVs reverts to wild-type colony morphology and showed true reversion, i.e. restoration of wild-type genotype. The results suggest that we are observing phase variation in Xoo. We hypothesize that similar phase variation may be a part of Xoo’s life cycle. Which may help the bacteria survive in nutrient limited conditions during late stages of infection and on rice seeds and plant debris.
Xanthomonas oryzae pv. oryzae XopQ protein suppresses rice immune responses through interaction with two 14-3-3 proteins but its phospho-null mutant induces rice immune responses and interacts with another 14-3-3 protein
(John Wiley & Sons, 2019) Deb, Sohini; Gupta, Mahesh K.; Patel, Hitendra K.; Sonti, Ramesh V.
Many bacterial phytopathogens employ effectors secreted through the type-III secretion system to suppress plant innate immune responses. The Xanthomonas type-III secreted non-TAL effector protein Xanthomonas outer protein Q (XopQ) exhibits homology to nucleoside hydrolases. Previous work indicated that mutations which affect the biochemical activity of XopQ fail to affect its ability to suppress rice innate immune responses, suggesting that the effector might be acting through some other pathway or mechanism. In this study, we show that XopQ interacts in yeast and in planta with two rice 14-3-3 proteins, Gf14f and Gf14g. A serine to alanine mutation (S65A) of a 14-3-3 interaction motif in XopQ abolishes the ability of XopQ to interact with the two 14-3-3 proteins and to suppress innate immunity. Surprisingly, the S65A mutant gains the ability to interact with a third 14-3-3 protein that is a negative regulator of innate immunity. The XopQS65A mutant is an inducer of rice immune responses and this property is dominant over the wild-type function of XopQ. Taken together, these results suggest that XopQ targets the rice 14-3-3 mediated immune response pathway and that its differential phosphorylation might enable interaction with alternative 14-3-3 proteins.